What Is the Role of Transaction Confirmation Depth in Preventing Double-Spends?

Confirmation depth is the number of blocks added to the chain after the block containing a specific transaction. Each subsequent block makes it exponentially harder for an attacker to reorganize the chain and reverse the transaction.

A high confirmation depth (e.g. 6 blocks for Bitcoin) is the standard defense against double-spends, as it makes the cost of reversing the transaction prohibitively high, relying on the probabilistic finality of the PoW system.